U.S. patent number 6,187,691 [Application Number 09/570,195] was granted by the patent office on 2001-02-13 for method of forming film on semiconductor substrate in film-forming apparatus.
This patent grant is currently assigned to ASM Japan K.K.. Invention is credited to Hiroki Arai, Hideaki Fukuda, Yu Yoshizaki.
United States Patent |
6,187,691 |
Fukuda , et al. |
February 13, 2001 |
Method of forming film on semiconductor substrate in film-forming
apparatus
Abstract
A thin film is formed on a substrate in a film-forming apparatus
which has upper and lower electrodes between which radio-frequency
power is applied in a processing chamber, and a heater is used to
heat the lower electrode on which the substrate is loaded. In one
lot, at least one substrate is processed. The electrode is heated
at the end of a stand-by period between lots and before starting
the film-forming process.
Inventors: |
Fukuda; Hideaki (Tama,
JP), Arai; Hiroki (Tama, JP), Yoshizaki;
Yu (Tama, JP) |
Assignee: |
ASM Japan K.K. (Tokyo,
JP)
|
Family
ID: |
15119736 |
Appl.
No.: |
09/570,195 |
Filed: |
May 15, 2000 |
Foreign Application Priority Data
|
|
|
|
|
May 14, 1999 [JP] |
|
|
11-134072 |
|
Current U.S.
Class: |
438/758;
257/E21.293; 427/585; 427/588; 438/905; 438/778 |
Current CPC
Class: |
C23C
8/36 (20130101); C23C 16/4405 (20130101); H01L
21/3185 (20130101); C23C 16/54 (20130101); Y10S
438/905 (20130101) |
Current International
Class: |
C23C
16/44 (20060101); C23C 8/06 (20060101); C23C
8/36 (20060101); C23C 16/54 (20060101); H01L
21/318 (20060101); H01L 21/02 (20060101); H01L
21/314 (20060101); H01L 021/31 (); C23C
008/00 () |
Field of
Search: |
;438/758,778,905
;427/585,588 ;118/723E |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bowers; Charles
Assistant Examiner: Ghyka; Alexander G.
Attorney, Agent or Firm: Knobee, Martens, Olson & Bear,
LLP
Claims
What is claimed is:
1. A method of forming a thin film on a substrate in a film-forming
apparatus comprising upper and lower electrodes in a processing
chamber, between which radio-frequency power is applied, wherein a
film-forming process is conducted at a designated temperature on a
substrate loaded on the lower electrode which is provided with a
heater, and in one lot, at least one substrate is processed, said
method comprising:
at the end of a stand-by period in which no film forming is
performed between lots and before initiating the film-forming
process, heating the lower electrode to a temperature close to the
temperature for film forming.
2. The method as claimed in claim 1, wherein in one lot, multiple
substrates are continuously processed.
3. The method as claimed in claim 1, wherein the heater and the
lower electrode are not integrated, and the heating step is
conducted not only by using the heater but also by supplying gas
into the processing chamber to increase heat conductivity between
the heater and the electrode.
4. The method as claimed in claim 3, wherein the pressure of gas
supplied into the processing chamber is no less than 1 Torr.
5. The method as claimed in claim 3, wherein the gas supplied into
the processing chamber is a cleaning gas activated by a remote
plasma discharge apparatus.
6. The method as claimed in claim 1, wherein the heating step is
conducted by generating plasma by supplying a reaction gas into the
processing chamber.
7. The method as claimed in claim 6, wherein the plasma-generating
step further comprises forming a dummy film on the lower electrode
at lower radiofrequency power than when film forming is conducted
on a substrate.
8. The method as claimed in claim 7, wherein the plasma-generating
step further comprises dummy-cleaning the dummy film formed on the
electrode, wherein heat is generated when a reaction occurs between
the dummy film and a cleaning gas for dummy-cleaning.
9. The method as claimed in claim 8, wherein the dummy-cleaning
process is conducted by supplying into the processing chamber a
cleaning gas activated by a remote plasma discharge apparatus.
10. The method as claimed in claim 7, further comprising supplying
gas into the processing chamber after the dummy-cleaning
process.
11. The method as claimed in claim 1, wherein the heating step is
completed before completion of the loading of a substrate on the
electrode.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a film-forming method of forming a
thin film on a substrate-to-be-processed. It particularly relates
to a film-forming method of homogenizing a thin film formed on each
substrate-to-be-processed when forming a thin film continuously on
multiple substrates-to-be-processed.
2. Description of the Related Art
A plasma CVD (Chemical Vapor Deposition) apparatus forms a thin
film on the surface of a substrate-to-be-processed by applying
radio-frequency power between an upper electrode, which also
functions as a showerhead which supplies a reaction gas to a
processing chamber, and a lower electrode which also functions as a
loading platform for loading substrates-to-be-processed such as
semiconductor wafers. Sediment is left on inner walls, etc. of the
processing chamber during this film-forming process. If this comes
off, it causes particle contamination in the next film-forming
process. For this reason, the processing chamber is cleaned
periodically.
For such apparatuses, when a lot (one lot can be, for example, one
cassette (25 wafers)) is processed continuously, the film-forming
process and the cleaning process are repeated alternately. After
maintenance of the apparatus is performed, until the result of a
film quality inspection of wafer processing is obtained, a stand-by
situation where no film forming is performed occurs between the lot
processes.
The number of stand-by times shows a tendency to increase
particularly as the number of semiconductor manufacturing plants
which manufacture semiconductor devices with more different types
in smaller lots increases, as a diameter of wafer becomes larger in
recent years, and as semiconductor devices are more
diversified.
SUMMARY OF THE INVENTION
If this stand-by situation continues for a certain time, a surface
temperature of electrode parts on which a semiconductor wafer is
loaded drops and a temperature of the wafer loaded on it also
drops. Consequently, even if other processing conditions are set
identically, in the continuous lot process, it causes a negative
influence such as a decline in density and change in film
composition on a thin film formed on the first and the second
semiconductor wafers after the stand-by period. For this reason,
film characteristics such as workability and hygroscopicity
resistance, which are designed when a semiconductor device is
manufactured, are spoiled. This eventually results in malfunction
of the semiconductor device, i.e., a cause of defective products
and a decline in yield.
The negative influence on film-forming occurring immediately after
stand-by has become serious due to increased heat capacity of a
wafer itself as a diameter of the wafer which is a
substrate-to-be-processed recently increases.
The present invention was achieved to solve this task, and it aims
to provide a film-forming method which prevents a negative
influence on the characteristics of film forming caused by a drop
in a temperature of an electrode which is a loading platform for
loading a substrate-to-be-processed.
Another object of the present invention is to provide the
above-mentioned film-forming method which forms a homogeneous film
during continuous lot processing.
The film-forming method according to the present invention which
achieves the above-mentioned objects has upper and lower electrodes
in a processing chamber, between which radio-frequency power is
applied, and which forms a thin film on a substrate-to-be-processed
in a film-forming apparatus which heats an electrode on which the
substrate-to-be-processed is loaded, and which is characterized in
that at the end of a stand-by period and before the film-forming
process is initiated by loading a substrate-to-be-processed on the
electrode, a process of raising a temperature of the lower
electrode is included. This film-forming process can be a
continuous film-forming process where after stand-by, a
substrate-to-be-processed is conveyed and is loaded on the
electrode and the film-forming process is performed continuously on
multiple substrates-to-be-processed. In an embodiment, the
temperature of the lower electrode reaches a temperature for
continuous film formation .+-. approximately 5.degree. C. In the
above, when it is not technically practical to measure the
temperature of the electrode to confirm that the temperature
reaches a desired temperature, by monitoring the thickness of films
formed on substrates, it is possible to determine whether the
temperature control is appropriate based on uniformity of thickness
of the formed films. Incidentally, the temperature of the electrode
is considered to be 5-10.degree. C. higher than the temperature of
a substrate placed thereon.
A heater heats an electrode on which a substrate-to-be-processed is
loaded and raises a temperature to a desired level. If the
electrode and the heater are not incorporated (when they are
divided by being fastened with screws, etc.), a temperature of the
electrode cannot be raised quickly to a desired level (a
temperature for film formation .+-. approximately 5.degree. C.). At
this time, by supplying gas to a processing chamber, the heat of
the heater can be effectively transmitted to the electrode on which
a substrate-to-be-processed is loaded and the electrode can be
heated quickly. For example, the pressure of the chamber is
maintained conventionally at several mTorr during a stand-by period
until a first substrate is loaded in the chamber, and thus even if
the temperature of the heater is set at 420.degree. C., the
temperature of the lower electrode (susceptor) has decreased to
320-350.degree. C. at the end of the stand-by period. By raising
the pressure of the chamber, heat transfer from the heater to the
lower electrode can be improved significantly. In the above, the
temperature of the lower electrode can be approximately 50.degree.
C. higher than the conventional embodiment.
In the above, for the pressure of the processing chamber with gas
supplied, pressure no less than 1 Torr is preferable (in an
embodiment, 4.+-.1 Torr). Gas to be supplied to the processing
chamber can be a cleaning gas which is activated by a remote plasma
discharge apparatus.
Additionally, a process of raising the temperature of the electrode
can be a process of supplying gas including a reaction gas into the
processing chamber and generating plasma. Further, the process of
raising the electrode temperature can include a process of
dummy-cleaning a dummy film on the electrode, which is formed by
this plasma. In this case, for example, when a silicon nitride film
is formed, gas which contains more than one type of gas containing
fluorine such as NF.sub.3 is excited by a remote plasma apparatus
and is brought in the processing chamber and a dummy film is
removed by dummy cleaning. Because of heat generated at the
reaction of the film and the cleaning gas, a surface temperature of
the electrode rises effectively. Moreover, after the dummy-cleaning
process, a process of supplying gas to the processing chamber can
be included.
Furthermore, if a process of raising temperature of the electrode
is performed before a substrate-to-be-processed is conveyed to the
processing chamber, processing time can be shortened.
For purposes of summarizing the invention and the advantages
achieved over the prior art, certain objects and advantages of the
invention have been described above. Of course, it is to be
understood that not necessarily all such objects or advantages may
be achieved in accordance with any particular embodiment of the
invention. Thus, for example, those skilled in the art will
recognize that the invention may be embodied or carried out in a
manner that achieves or optimizes one advantage or group of
advantages as taught herein without necessarily achieving other
objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will
become apparent from the detailed description of the preferred
embodiments which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of this invention will now be described
with reference to the drawings of preferred embodiments which are
intended to illustrate and not to limit the invention.
FIG. 1 roughly shows a cross section of a parallel-plate type
plasma CVD apparatus by which the present invention is
implemented.
FIG. 2(1) shows a series of processes of a conventional
film-forming method.
FIG. 2(2) shows a series of processes of the film-forming method
according to the present invention.
FIG. 3(a) shows change in film thickness when the lot process is
performed according to the conventional method. FIG. 3(b) shows
change in a refractive index when the lot process is performed
according to the conventional method. FIG. 3(c) shows change in
film stress when the lot process is performed according to the
conventional method.
FIG. 4(a) shows change in film thickness when the lot process is
performed according to the method of the present invention.
FIG. 4(b) shows change in a refractive index when the lot process
is performed according to the method of the present invention.
FIG. 4(c) shows change in film stress when the lot process is
performed according to the method of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a parallel-plate type plasma CVD apparatus which is
one example of an apparatus to implement the present invention. In
addition to this, for example, in a reduced pressure thermal CVD
apparatus with the same configuration as this type, the present
invention can be implemented.
The CVD apparatus in FIG. 1 has a configuration of performing
remote plasma cleaning for cleaning the processing chamber.
To perform a process of forming a film on one lot of
semiconductor-processing substrates (25 semiconductor wafers) using
this apparatus, the following operations are performed.
After the above-mentioned stand-by, one piece of
semiconductor-processing substrate 3 which is placed within a
transfer chamber 1 is loaded on a susceptor 5 within the processing
chamber 4 adjacent to the conveying chamber 1 by an auto transfer
robot 2. The susceptor 5 is an electrode equipped with a heater
(heating element) 9 embedded therein. A reaction gas is evenly
supplied on the substrate-to-be-processed from a showerhead 6 which
is parallel to the susceptor 5. Radio-frequency power is applied
between the susceptor 5 and the showerhead 6 by a radio-frequency
oscillator 7.
For example, when a silicon nitride film is formed on a silicon
substrate 3, a mixed gas of SiH.sub.4 and NH.sub.3 and N.sub.2 is
supplied as a reaction gas from the showerhead 6 to the processing
chamber 4. The pressure within the processing chamber is controlled
and adjusted to be within the scope of 1.about.8 Torr using a
conductance regulating valve 8 linked to the processing chamber 4.
The susceptor 5 on which a substrate-to-be-processed is loaded is
heated by a heater and the substrate-to-be-processed 3 is heated to
300.about.400.degree. C. (572.about.752.degree. F.) by being loaded
on the susceptor. Radio-frequency power of 13.56 MHz or mixed power
of 13.56 MHz and 430 MHz is applied between the susceptor 5 and the
showerhead 6. By plasma generated from this power, a thin film is
formed on the substrate and after the thin film is formed, the
substrate is conveyed out from the processing chamber 4 by the auto
transfer robot 2.
To remove unwanted products (silicon nitride in this example) which
adhere to the processing chamber 4 after the film is formed,
NF.sub.3 gas is brought in with argon to the remote plasma
discharge chamber 10, radio-frequency output is applied there, and
the gases are dissociated and activated. Activated cleaning gases
are brought in the processing chamber 4 through a valve 11 and with
these gases, cleaning of the inside of the processing chamber is
performed.
The film-forming process and cleaning process are performed
alternately for each lot.
EXAMPLES
In the following, comparison between a conventional method and a
method according to the present invention is explained using
specific examples:
In a conventional method using an apparatus shown in FIG. 1, as
mentioned in the above regarding the processing of one lot, after
the stand-by period, the film-forming process and the cleaning
process are performed alternately (Refer to FIG. 2(1)). For
processing conditions at this time, the conditions for the
film-forming process are shown in Table 1 and the conditions for
the cleaning process are shown in Table 2. Further, for the
film-forming time and the cleaning time, the time required for
forming a silicon nitride film of 580 nm and for cleaning the
inside of the processing chamber are set.
TABLE 1 Set values at film-forming processing Silane (sccm) 220
Ammonia (sccm) 1100 Nitrogen (sccm) 600 Argon (sccm) 100 Pressure
in reaction chamber (Torr) 3.75 13.56 MHz Power (W) 480 430 KHz
Power (W) 185 Heater temperature (.degree. C./.degree. F.) 420/788
Electrode spacing (mm) 10 Time (sec) 50
TABLE 2 Set values at cleaning processing Nitrogen trifluoride
(sccm) 680 Argon (sccm) 1020 Pressure in reaction chamber (Torr) 4
Heater temperature (.degree. C./.degree. F.) 420/788 Electrode
spacing (mm) 14 Time (sec) 15
Using the conventional method, a silicon nitride film is
continuously processed for one lot (25 pieces of
substrates-to-be-processed), in other words, after a certain
stand-by period, when the film-forming process of the first
substrate is performed, then cleaning of the inside of the
processing chamber is performed and the film-forming process and
the cleaning process are performed alternately after the second
substrate. Change in the quality of the film formed on the
substrates is shown in FIG. 3. FIG. 3 shows change in film
thickness (a), change in a refractive index (b) and change in film
stress (c).
As seen from FIG. 3, as compared with the film of the third
substrate processed and those processed thereafter, the films of
the first and second substrates processed are thicker and have a
lower refractive index and smaller compression stress (particularly
in the case of the first substrate). This indicates that after
stand-by, a surface temperature of the susceptor on which the
substrate-to-be-processed was loaded was lower than a temperature
of the susceptor in the continuous film-forming process which
followed.
Consequently, to perform a uniform process, it is necessary to
improve the process on the first and second
substrates-to-be-processed after the stand-by, particularly to
improve the process on the first one. In other words, after the
stand-by period, it is necessary to prevent a temperature of the
substrate-to-be-processed from dropping due to a temperature drop
in the susceptor.
The evenness of plasma silicon nitride films between the
substrates, which were formed on 25 substrates processed by this
conventional film-forming method, was .+-.2.03% according to the
following formula:
This .+-.2.03% value corresponds to an actual film thickness
difference of approximately 23 nm. However, as mentioned
previously, because forming the silicon nitride film of 580 nm is
set in this example, the film thickness of the first substrate in
which the maximum film thickness value is produced is approximately
600 nm.
In the above, after the silicon nitride film is formed on the first
substrate as its final protection film, if fine-structure formation
(etching process) is conducted by dry etching on a portion
contacting wiring formed below the protection film, wherein the
precision of the etching is the same as that of the silicon nitride
film formation, i.e., a precision of approximately 580.about.590
nm, a portion of the film having a thickness of 10.about.20 nm will
remain unremoved. This causes contact failure on the entire
apparatus on the substrate.
To prevent this contact failure from occurring, it is preferable
that the film uniformity between the substrates is at least a value
below .+-.1.5%.
Each example of the film-forming method according to the present
invention, which was implemented to prevent a negative influence,
caused by a temperature drop in a substrate-to-be-processed due to
the susceptor's temperature drop, from being exerted the film
quality of the first and the second substrates, as stated above, is
Table 3 below.
TABLE 3 Film Dummy Rising of Rising of Thickness Film Dummy Chamber
Heater Uniformity Process Forming Cleaning Pressure Temperature
(.+-. %) 1 X X X X 2.03 2 O X X X 1.30 3 O O X X 1.05 4 O O O X
0.35 5 X X O O 1.32 6 X O X O 0.82 X: Not implemented O:
Implemented
1 in Table 3 shows a conventional film-forming method which does
not take any measures against a surface temperature drop in the
susceptor. In this conventional example, the film thickness
uniformity between substrates is .+-.2.03% as mentioned above.
2 in Table 3 shows the case where before a
substrate-to-be-processed is conveyed in the processing chamber, a
reaction gas for film forming is brought in, plasma is generated,
film forming, i.e., dummy film forming, is conducted on the
electrode and a surface temperature of the electrode on which the
substrate-to-be-processed is loaded is raised. Film-forming
conditions at this time are shown in Table 4. Further, in this
case, to prevent abnormal electric discharge and electrode damage
from occurring, lower radio-frequency power and a wider electrode
spacing as compared with normal film-forming conditions (Table 1)
are used. As a result, the film-thickness uniformity between the
substrates improved to .+-.1.30%.
TABLE 4 Set value at dummy film forming Silane (sccm) 220 Ammonia
(sccm) 1100 Nitrogen (sccm) 600 Argon (sccm) 100 Pressure in
reaction chamber (Torr) 3.75 13.56 MHz Power (W) 300 430 KHz Power
(W) 0 Heater temperature (.degree. C./.degree. F.) 420/788
Electrode spacing (mm) 14 Time (sec) 30
3 in Table 3 shows the case where after the above-mentioned dummy
film-forming was conducted, dummy cleaning to remove the dummy film
was conducted. The silicon nitride film on the surface of the
electrode, which was formed by dummy film-forming, and a gas
excited by remote plasma were brought in the processing
chamber.
The surface temperature of the electrode further rose by reaction
heat generated at the time of removing the film by fluoride
radicals and the film-thickness uniformity between the substrates
improved up to .+-.1.05%. Additionally, because gas which was
excited by remote plasma was used, there was no plasma damage on
electrode parts and other parts.
4 in Table 3 shows the case where after the above-mentioned dummy
cleaning, nitrogen gas was brought in the processing chamber at the
set value shown in Table 5. In this case, if a heater and an
electrode are not incorporated, thermal conduction from the heater
to the electrode becomes better and a temperature of the electrode
(the susceptor) on which a substrate-to-be-processed is loaded
rises. The film-thickness uniformity between the substrates at this
time improved to .+-.0.35%. Further, the gas brought in here is not
limited to nitrogen gas and various gases can be used.
Change in film thickness, change in a refractive index and change
in film stress when a lot was processed after this pre-process was
performed are shown in FIG. 4. As seen if comparing this figure
with FIG. 3 which shows the case of the conventional method, for
either of the film thickness, the refractive index and the film
stress, no abnormal film quality was observed for the first and the
second substrates after stand-by.
TABLE 5 Set values at pressure rising in the reaction chamber
Nitrogen (sccm) 100 Pressure in reaction chamber (Torr) 8 Heater
temperature (.degree. C./.degree. F.) 420/788 Electrode spacing
(mm) 10 Time (sec) 40
5 and 6 in Table 3 show the respective cases where a temperature of
the heater was initially set high (at 430.degree. C.; 10.degree. C.
higher than a temperature set for continuous film formation or
regular stand-by, 420.degree. C.) and nitrogen gas and the
above-mentioned dummy cleaning gas were brought in the processing
chamber. In the same way as mentioned above, the gases brought in
improve thermal conduction from the heater to the electrode and a
temperature of the electrode (the susceptor) on which a
substrate-to-be-processed is loaded rises. The film-thickness
uniformity between the substrates at this time improved to
.+-.1.32% and .+-.0.82% respectively.
Table 3 shows examples of raising a susceptor temperature according
to the present invention. In addition to the examples listed here,
those in the trade could easily conclude that various combinations
of each process would be possible. Furthermore, it could be
understood that values for the processes could be set.
Additionally, it is preferable that pre-processes before film
forming are performed after the start of the operation of the
apparatus and before the first substrate-to-be-processed is
conveyed in, because the pre-processes do not lower processing
throughput.
[The Efficacy of the Present Invention]
With the present invention, a temperature drop in the surface of
the electrode on which a substrate-to-be-processed is loaded can be
prevented and, as a result, desired film forming can be
achieved.
Because the present invention accommodates various sizes of
substrates-to-be-processed which are loaded on the electrode,
desired film forming can be achieved, for example, even if the heat
capacity of a wafer itself increases as a diameter of a
semiconductor wafer becomes larger, as in recent years. Further,
the present invention can be applied if the number of stand-by
periods increases where many types of semiconductor devices are
manufactured in small lots or batches.
Moreover, in batch processes, when the film-forming process is
performed on multiple substrates-to-be-processed, homogeneous
film-forming can be achieved on each substrate by following the
present invention. Particularly, because a thin film of uniform
thickness can be formed on each substrate, yield in semiconductor
device manufacturing can be improved and reliability can be
improved.
Furthermore, by raising the surface temperature of the electrode
according to the present invention before the first
substrate-to-be-processed is conveyed in the processing chamber,
desired film forming can be achieved without incurring a decline in
productivity.
It will be understood by those of skill in the art that numerous
and various modifications can be made without departing from the
spirit of the present invention. Therefore, it should be clearly
understood that the forms of the present invention are illustrative
only and are not intended to limit the scope of the present
invention.
* * * * *